Year	Age
1970	2.5
1971	2.6
1972	2.8
1973	2.9
1974	3.1
1975	3.3
1976	3.4
1977	3.6
1978	3.8
1979	4
1980	4.2
1981	4.4
1982	4.6
1983	4.9
1984	5.1
1985	5.3
1986	5.5
1987	5.8
1988	6
1989	6.2
1990	6.4
1991	6.7
1992	6.9
1993	7.1
1994	7.3
1995	7.5
1996	7.7
1997	8
1998	8.2
1999	8.4
2000	8.6
2001	8.8
2002	8.9
2003	9.1
2004	9.3
2005	9.5
2006	9.7
2007	9.8
2008	10
2009	10.1